274 I'liosriioRic oxide in i-ertilisees. 



purcliase such mixtuies, more especially in Rliodesia, owing 

 to the high ocean and railway freights. 



The greatest loss of water-soluble phosphoric oxide, as 

 Avas naturally to be expected, occurs in the limestone mixture. 

 It can safely be said that chemical action starts immediately, 

 and is continuous. After being mixed for three weeks the 

 loss amounts to as much as 98 per cent., Gray's mixture at 

 the end of eighteen day.s amounts to 86 per cent., and 

 Brackett's after approximately five months to 87 per cent. 



Burgest (4), State Agronomist of North Carolina, has 

 recommended a mixture of 1,200 pounds of ground limestone 

 to from 400 to 1,000 pounds of superphosphate. 



The loss in rcA-ersion with mixtures of superphosphate 

 and ashes vary greatly — from 52 to over 84 per cent, was 

 obtained during a period of three weeks — the least reversion 

 occurring with ash from sea plants, as agaiuvst the highest with 

 plant ash. This is due to the fact tliat the ash of sea plants 

 contains less carbonates. 



The mixtures with ashes should be of interest to 

 merchants offering for sale compound or complete fertilisers 

 when employed for making' up the potash content. 



The amount of reversion of water-soluble phosphoric 

 oxide in mixtures such as above would vary considerably, 

 due to the amount of lime in combination as oxide, hydrate 

 or carbonate in the materials used for mixing purposes. 



COXCLITSIOXS. 



Superphosphate should not be mixed with mineral phos- 

 phate, basic slag, Ephos basic phosphate, limestone or ashes, 

 on account of reversion of water-soluble phosphoric oxide 

 to that of water-insoluble phosphoric oxide being likely to 

 take place at a very rapid rate in many instances. 



A mixture could be made in tire case of superphosphate 

 and mineral phosphate if the amount of lime combined as 

 carbonate is low in the untreated phosphate. The amount of 

 reversion in such a mixture would i)robably be proportional 

 to the amount of calcium carbonate present in the untreated 

 rock phosphate. 



REFEKKNCES. 



1. Scott Robertsox — 



The rate of reversion of mixtures of superpliospliate ^^ ith liasic 

 slag ;.nd rock phosphates. — Jourii. of Sc. of Chem. IiuL, vol. 

 xxxvi, pp. 626-628. 



2. Gray— 



Trdiisdctioiis of flic A u sfriilia n Association for the Advtinccincnt 

 of Science. Diinedin, January, 1904. 



3. Brackett — 



The action of calcium carbonate on acid phosphate. — E. W. 

 Magruder, Juurn. of Ind. and Eng. Chem.. vol. 9, p. 155. 



4. Burgest — 



Bulletin Xo. 220, Xoith Carolina Dcpt. of Arjric. 



